Amplifier dc bias protection circuit and related audio system

Abstract

An amplifier DC bias protection circuit includes an amplifier module, a filter module and a comparator module. The amplifier module converts an input signal into a non-inverting signal and an inverting signal. The filter module blocks AC signals in the non-inverting signal and the inverting signal, thereby providing a first DC bias signal and a second DC bias signal accordingly. The comparator module is configured to determine whether the absolute value of a DC bias difference signal is greater than a predetermined value, and output a determination signal for deactivating the amplifier module when the absolute value of the DC bias difference signal is greater than the predetermined value. The DC bias difference signal is associated with the voltage difference between the first DC bias signal and the second DC bias signal.

What is claimed is: 
     
         1 . An amplifier direct-current (DC) bias protection circuit, comprising:
 an amplifier module configured to convert an input signal into a non-inverting signal and an inverting signal;   a filter module configured to:
 block an alternative-current (AC) component in the non-inverting signal for providing a corresponding first DC bias signal; and 
 block an AC component in the inverting signal for providing a corresponding second DC bias signal; and 
   a comparator module configured to:
 determine whether an absolute value of a DC bias difference signal is greater than a predetermined value; and 
 output a determination signal for deactivating the amplifier module when the absolute value of the DC bias difference signal is greater than the predetermined value, wherein the DC bias difference signal is associated with a voltage difference between the first DC bias signal and the second DC bias signal. 
   
     
     
         2 . The amplifier DC bias protection circuit of  claim 1 , wherein the amplifier module comprises:
 a first operational amplifier module configured to provide the non-inverting signal by amplifying the input signal with a first gain having a positive value; and   a second operational amplifier module configured to provide the inverting signal by amplifying the input signal with a second gain having a negative value.   
     
     
         3 . The amplifier DC bias protection circuit of  claim 2 , wherein:
 the amplifier module further comprises a first resistor, a second resistor, a third resistor, and a fourth resistor;   the first operational amplifier comprises:
 a non-inverting input end coupled to the input signal; 
 an inverting input end coupled to a ground voltage via the first resistor; and 
 an output end coupled to the inverting input end of the first operational amplifier via the second resistor for outputting the non-inverting signal; and 
   the second operational amplifier comprises:
 a non-inverting input end coupled to the ground voltage; 
 an inverting input end coupled to the input signal via the third resistor; and 
 an output end coupled to the inverting input end of the second operational amplifier via the fourth resistor for outputting the inverting signal. 
   
     
     
         4 . The amplifier DC bias protection circuit of  claim 1 , wherein the filter module comprises:
 a fifth resistor, including:
 a first end coupled to the amplifier module for receiving the non-inverting signal; and 
 a second end for outputting the first DC bias signal; 
   a sixth resistor, including:
 a first end coupled to the amplifier module for receiving the inverting signal; and 
 a second end for outputting the second DC bias signal; 
   a first capacitor coupled between the second end of the fifth resistor and a ground voltage; and   a second capacitor coupled between the second end of the sixth resistor and the ground voltage.   
     
     
         5 . The amplifier DC bias protection circuit of  claim 1 , wherein the comparator module comprises a third operational amplifier module configured to provide the DC bias difference signal by amplifying the voltage difference between the first DC bias signal and the second DC bias signal with a third gain. 
     
     
         6 . The amplifier DC bias protection circuit of  claim 5 , wherein:
 the comparator module further comprises a seventh resistor, an eighth resistor, a ninth resistor, and a tenth resistor;   the third operational amplifier comprises:
 a non-inverting input end coupled to the first DC bias signal via the seventh resistor; 
 an inverting input end coupled to the second DC bias signal via the ninth resistor; and 
 an output end coupled to the inverting input end of the third operational amplifier via the tenth resistor for outputting the DC bias difference signal. 
   
     
     
         7 . The amplifier DC bias protection circuit of  claim 6 , wherein the comparator module further comprises:
 a first comparator configured to provide a first comparison signal according to a relationship between the DC bias difference signal and a threshold voltage, and comprising:
 a non-inverting input end coupled to the output end of the third operational amplifier for receiving the DC bias difference signal; 
 an inverting input end coupled to the threshold voltage; and 
 an output end for outputting the first comparison signal; and 
   a second comparator configured to provide a second comparison signal according to a relationship between an inverting DC bias difference signal and the threshold voltage, and comprising:
 a non-inverting input end coupled to the inverting DC bias difference signal which is an inverting signal of the DC bias difference signal; 
 an inverting input end coupled to the threshold voltage; and 
 an output end for outputting the second comparison signal. 
   
     
     
         8 . The amplifier DC bias protection circuit of  claim 7 , wherein the comparator module further comprises an inverter configured to convert the DC bias difference signal into the inverting DC bias difference signal. 
     
     
         9 . The amplifier DC bias protection circuit of  claim 7 , wherein the comparator module further comprises an judging circuit configured to output the determination signal according to a voltage level of the first comparison signal and a voltage level of the second comparison signal. 
     
     
         10 . The amplifier DC bias protection circuit of  claim 9 , wherein the judging circuit is an exclusive-OR gate which includes:
 a first input end coupled to the output end of the first comparator for receiving the first comparison signal;   a second input end coupled to the output end of the second comparator for receiving the second comparison signal; and   an output end for outputting the determination signal.   
     
     
         11 . An audio system which provides signal amplification and direct-current (DC) bias protection, comprising:
 a speaker module; and   an amplifier DC bias protection circuit, comprising:
 an amplifier module configured to convert an input signal into a non-inverting signal and an inverting signal for driving the speaker module; 
 a filter module configured to:
 block an alternative-current (AC) component in the non-inverting signal for providing a corresponding first DC bias signal; and 
 block an AC component in the inverting signal for providing a corresponding second DC bias signal; and 
 
 a comparator module configured to:
 determine whether an absolute value of a DC bias difference signal is greater than a predetermined value; and 
 output a determination signal for deactivating the amplifier module when the absolute value of the DC bias difference signal is greater than the predetermined value, wherein the DC bias difference signal is associated with a voltage difference between the first DC bias signal and the second DC bias signal. 
 
   
     
     
         12 . The audio system of  claim 11 , wherein the amplifier module comprises:
 a first operational amplifier module configured to provide the non-inverting signal by amplifying the input signal with a first gain having a positive value; and   a second operational amplifier module configured to provide the inverting signal by amplifying the input signal with a second gain having a negative value.   
     
     
         13 . The audio system of  claim 12 , wherein:
 the amplifier module further comprises a first resistor, a second resistor, a third resistor, and a fourth resistor;   the first operational amplifier comprises:
 a non-inverting input end coupled to the input signal; 
 an inverting input end coupled to a ground voltage via the first resistor; and 
 an output end coupled to the inverting input end of the first operational amplifier via the second resistor for outputting the non-inverting signal; and 
   the second operational amplifier comprises:
 a non-inverting input end coupled to the ground voltage; 
 an inverting input end coupled to the input signal via the third resistor; and 
 an output end coupled to the inverting input end of the second operational amplifier via the fourth resistor for outputting the inverting signal. 
   
     
     
         14 . The audio system of  claim 11 , wherein the filter module comprises:
 a fifth resistor, including:
 a first end coupled to the amplifier module for receiving the non-inverting signal; and 
 a second end for outputting the first DC bias signal; 
   a sixth resistor, including:
 a first end coupled to the amplifier module for receiving the inverting signal; and 
 a second end for outputting the second DC bias signal; 
   a first capacitor coupled between the second end of the fifth resistor and a ground voltage; and   a second capacitor coupled between the second end of the sixth resistor and the ground voltage.   
     
     
         15 . The audio system of  claim 11 , wherein the comparator module comprises a third operational amplifier module configured to provide the DC bias difference signal by amplifying the voltage difference between the first DC bias signal and the second DC bias signal with a third gain. 
     
     
         16 . The audio system of  claim 15 , wherein:
 the comparator module further comprises a seventh resistor, an eighth resistor, a ninth resistor, and a tenth resistor;   the third operational amplifier comprises:
 a non-inverting input end coupled to the first DC bias signal via the seventh resistor; 
 an inverting input end coupled to the second DC bias signal via the ninth resistor; and 
 an output end coupled to the inverting input end of the third operational amplifier via the tenth resistor for outputting the DC bias difference signal. 
   
     
     
         17 . The audio system of  claim 16 , wherein the comparator module further comprises:
 a first comparator configured to provide a first comparison signal according to a relationship between the DC bias difference signal and a threshold voltage, and comprising:
 a non-inverting input end coupled to the output end of the third operational amplifier for receiving the DC bias difference signal; 
 an inverting input end coupled to the threshold voltage; and 
 an output end for outputting the first comparison signal; and 
   a second comparator configured to provide a second comparison signal according to a relationship between an inverting DC bias difference signal and the threshold voltage, and comprising:
 a non-inverting input end coupled to the inverting DC bias difference signal which is an inverting signal of the DC bias difference signal; 
 an inverting input end coupled to the threshold voltage; and 
 an output end for outputting the second comparison signal. 
   
     
     
         18 . The audio system of  claim 17 , wherein the comparator module further comprises an inverter configured to convert the DC bias difference signal into the inverting DC bias difference signal. 
     
     
         19 . The audio system of  claim 17 , wherein the comparator module further comprises an judging circuit configured to output the determination signal according to a voltage level of the first comparison signal and a voltage level of the second comparison signal. 
     
     
         20 . The audio system of  claim 19 , wherein the judging circuit is an exclusive-OR gate which includes:
 a first input end coupled to the output end of the first comparator for receiving the first comparison signal;   a second input end coupled to the output end of the second comparator for receiving the second comparison signal; and   an output end for outputting the determination signal.